Cessna 172 pilot reported a near mid air collision while conducting an engine conditioning flight. The pilot performed evasive maneuvers and then continued to home airport.

Narrative

While executing normal conditioning of a new engine; I flew my aircraft around a sparsely populated area at 1500 ft. MSL that allowed for immediate options for landing in the event of a forced landing and that would be readily accessible to emergency responders. This section to conduct the conditioning in was chosen for its noise abatement quality; availability for forced landing locations and its isolation in the practice area. This landmark is not traditionally used for low altitude operations and was deemed to be a safe area to make repeated laps around. While making my laps around the predetermined area; I made multiple position and intention calls over the common practice area advisory frequency. The whole flight; I maintained visual separation with other aircraft and took precautionary action when necessary to remain clear of traffic. I implemented turn clearing procedures and collision avoidance techniques throughout the flight per the operator's recommended method and personal scanning techniques. When making a turn around my point; I was alerted of an aircraft at a nearby position returning from the practice area to the airport to the North. The call came from a nearby point in the practice area. Having a visual on the area; I scanned the area and surroundings thoroughly. Having found no hazards; I proceeded with my clockwise turn to the South. Having made multiple radio calls to this time and within a short time of the incident; I maintained my scan and previously known position within my last known location as to keep my position accurate to other aircraft. The other calling aircraft returning from the practice area was on a reciprocal heading to my own; my own being southbound and theirs northbound. The aircraft was obscured to my view by my nose cowling; only becoming apparent once within close proximity. The estimated encounter distance was within 350-400 ft. vertically below my position. The incident occurred at roughly XA:08 in VMC.The other aircraft was an unidentified Piper PA-28. The other aircraft responded to my transmission after the incident occurred; which consisted of a mutual recognition of the situation. Both flights continued safely. I shifted my operating area further South to avoid any crossing traffic between the airport and practice area and immediately advised the appropriate personnel at my flight school of the incident via a text message. Possible causes and suggestions are I believe the situation was caused by a variety of human factors and of being at a poor position relative to each other. There was a failure to recognize that the direct route between the returning aircraft; my position and the home airport was in an intersecting course. Being that both aircraft were converging head on; relative motion would not be easily recognized by either crew. Blind spots in the 172 would have obscured the aircraft's position while in the southbound turn and convergence course; leaving a large period of time for myself to be vulnerable. To prevent this a common corridor could be established and mutually agreed upon by operators in the practice area that separated transient; to and from traffic between the airport and practice area; and participating training aircraft. Increase awareness training of the practice area; its boundaries and conflicting routes between points. Encourage instructors and students to query fellow pilots on the frequency regarding positions to ensure everyone is on the same agreed upon plans and intentions. Increase blind spot awareness in a congested flight training area.